• International Journal of Safety
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• 제5권1호
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• pp.10-16
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• 2006

A suspended hemispherical silicon asperity moving over a silicon plate was simulated. The simulation results on friction and wear in the interface between the two can help obtain more durable miscroscale structures. Silicon structures were constructed with Tersoff three-body potential. Dependence of friction and wear of the asperity on both the atomic arrangement in the plate and the moving direction was investigated under the condition that the asperity is subject to the attractive normal force due to the plate. The results show that the variation of friction force with the movement of asperity, and the occurrence of adhesive wear are attributed to the formation and rupture of asperity, junction between the asperity and the plate. The friction force and wear are smaller when the asperity is incommensurate with the plate, and they also depend on the moving direction of the asperity over the plate.

• 터널과지하공간
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• 제23권5호
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• pp.401-412
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• 2013

전단거동에 의한 절리면의 거칠기 변화가 전단강도에 미치는 영향을 조사하기 위하여 절리면 강도가 상이한 편마암, 화강암 및 셰일 시료를 이용하여 순차적 다단계 전단시험을 수행하였다. 시험단계별로 절리면 프로파일의 고도를 측정하여 거칠기 계수를 산정하고 미세 거칠기 빈도 변화를 조사하였다. 거칠기 감쇠에 대한 최적의 거칠기 계수를 산정하여 반복된 전단거동에 의한 순차적 거칠기 감쇠특성을 고찰하였다. 전단강도식을 산정하여 점착력과 마찰각의 차별적 변화양상을 도출하였으며, 표면 거칠기의 마모, 파쇄 및 재형성에 의한 미세 거칠기 빈도변화를 조사하여 강도계수 변화의 원인적 요인을 분석하였다. 또한, 미세 거칠기 변화양상이 전단강도에 미치는 영향을 절리면 강도를 고려하여 분석하였다.

• 대한기계학회논문집A
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• 제28권5호
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• pp.547-553
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• 2004

A hemispherical asperity moving over a flat plane is simulated based on classical molecular dynamics. The asperity and the plane consist of silicon atoms whose interactions are governed by the Tersoff three-body potential. The gap between the asperity and the plane is maintained to produce attractive normal force in order to investigate the adhesive friction and wear. The simulation focuses on the influence of crystallographic orientation of the contacting surfaces and the moving direction. It is demonstrated that the adhesive friction and wear are lower when crystallographic orientations of the contacting surfaces are different, and also depend on the moving direction relative to the crystal1ographic orientation.

• 한국터널지하공간학회 논문집
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• 제11권3호
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• pp.303-314
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• 2009

암석 절리면의 거칠기의 발현에 따른 돌출부의 손상 특성을 연구하기 위해 전단시험 한 절리면 시편에 대한 이미지 분석을 수행하였다. 동일한 절리면에 대한 반복적인 시험에는 복제 시편을 사용한 모델시험이 가장 적합하였으므로 암석절리면으로부터 각기 다른 4종류의 3차원 거칠기를 복제하고, 고강도 석고를 사용한 시편을 제작하였다. 연직응력 수준을 변화시키며 총 20여회의 전단시험을 실시하였으며, 전단된 시편의 디지털 사진의 이미지 분석을 통하여 손상된 거칠기의 국지적 양상과 규모를 분석하였다. 분석 결과 거칠기의 손상 특성은 연직응력의 수준에 크게 의존하며, 돌출부의 파괴와 마모로 규정할 수 있는 것으로 나타났다. 돌출부 손상은 첨두 전단변위에서 가장 많이 발생하며, 변위가 증가하면 작은 돌출부들이 새롭게 손상되어 평균적인 돌출부의 손상 규모는 일정한 것으로 나타났다. 고강도 석고를 사용한 전단시험 결과에 자연 암석절리의 돌출부를 구성하는 광물입자의 물리적 특성이 완전하게 반영될 수는 없다. 그러나 첨두 전단변위와 돌출부 손상과의 상관관계에 대한 정량적 연구 결과는 돌출부 손상 특성의 파악이 암석 절리면 역학적 특성과 전단모델의 연구에 매우 중요한 수단이 될 수 있음을 보여준다.

• 한국지반공학회논문집
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• 제38권2호
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• pp.29-38
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• 2022

마찰 방향에 따른 전단 저항의 이방성을 지반 구조물에서 선택적으로 이용할 수가 있다. 예를 들어서, 축방향으로 하중을 가하는 깊은 기초, 소일 네일링, 타이백 등은 큰 전단 저항이 유발되므로 하중 전달 능력을 증가시키지만, 이와 반대로 말뚝 관입과 흙 시료 채취 등은 최소화된 전단 저항만 유발된다. 기존 연구는 뱀 비늘의 기하학적 형상과 유사한 표면 돌출부를 갖는 플레이트와 흙 경계면에서 유발되는 전단 저항 변화를 확인하였다. 본 논문에서는 표면 돌출부의 형상에 따른 경계면 마찰각의 변화를 정량적으로 평가하였다. 수정된 직접 전단 시험기를 이용하여 상대 밀도가 40%로 조성된 모래 시료에 대해 9개의 플레이트, 2개의 전단 방향(전단 시 돌출부 높이가 증가와 감소하는 방향), 그리고 3개의 초기 수직 응력(100kPa, 200kPa, 300kPa) 조건으로 총 51가지 경우를 실험 하였다. 실험 결과, 전단 응력은 돌출부 높이가 높을수록, 돌출부 길이가 짧을수록, 돌출부 높이가 증가하는 전단 방향에서 크게 나타났다.

• Tribology and Lubricants
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• 제15권4호
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• pp.335-342
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• 1999

Corrosion of the disk has been an ongoing concern for the manufacturers of hard disk drives. With the advent of magnetoresistive (MR) head, very low levels of corrosion and contamination become more critical since the raised defects and corrosion products on the disk surface-anything that heats the MR sensor due to the contact-can distort the output signal of the head. This phenomenon is called as thermal asperity. In this paper, the effect of corrosion as a form of Co migration on the occurrence of thermal asperity in MR drives was investigated. The corrosion test at high temperature (60$^{\circ}C$) and high relative humidity (80%) was emphasized in this study and the testing results at ambient condition were compared. The corrosion on the disks was characterized as the amount of Co ion migration using an ion chromatography (IC) and a time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It is proved that corrosion on the disk surface after storage testing is closely correlated to the amount of Co ions migration from the magnetic layer to disk surfaces and higher Co migration causes more thermal asperities in the drive. In order to reduce Co migration, several methods such as burnishing process and structure of the carbon overcoat were investigated. It is found that the hydrogenated carbon overcoat shows the least Co migration among different types of overcoat layer. However, the most effective way to reduce Co migration is the application of Cr layer between the overcoat and the magnetic alloy layer.

• Tribology and Lubricants
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• 제10권4호
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• pp.75-81
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• 1994

In load sharing model, the load is supported by the contacting asperities and the lubricants. The asperity contact area of two sliding surfaces are relatively very small as compared with the apparent contact area. The asperity contact pressure is relatively higher than the lubricant pressure. With the combined effect of asperity and lubricant pressure, the surface roughness and temperature rise must be considered to calculate the lubricant film thickness of the line-contact bearing.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.57-58
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• 2002

Asperity arrays and Independent asperities were fabricated on a silicon plate. Then pull-off and friction forces were measured on each asperity pattern by using AFM (atomic force microscope) in humid air and high vacuum of $2{\times}10^{-5}$ Pa. The probe of AFM cantilever has a flat square of about $1\;{\mu}m^2$ on its tip. The results showed that the pull-off force was proportional to the curvature radius of asperity peak in each ambient condition. The friction force was proportional to the pull-off force and was slightly higher in the humid air than in the high vacuum.

• Tribology and Lubricants
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• 제21권6호
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• pp.289-295
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• 2005

Most machine element, such as gears and bearings, are operated in the mixed lubrication region. Contact between two asperities has an effect on machine life by increasing local pressure. To estimate fatigue life exactly, asperity contact should be considered as a factor of fatigue life because this happening produce friction, abrasion and make flash temperature. In this paper, asperity contact is considered as a result of film breakdown when lubricant pressure is not enough to separate two asperities. Contact pressure is calculated to asperity overlap region and added to lubricant pressure. For this model, numerical procedure is introduced and the result on surface roughness and velocity for wheel bearing is presented. Results of EHL analysis for wheel bearing show that asperity contact is occurred at the edge ofEHL conjunction where has a insufficient lubricant pressure to separate two surface.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.859-865
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• 2001

This paper reports on the theoretical analysis of mixed lubrication for the piston ring. The analytical model is presented by using the average flow and asperity contact model. The cyclic variations of the nominal minimum oil film thickness are obtained by numerical iterative method. The total friction is calculated by using the hydrodynamic and asperity contact theory. The effect of the roughness height, pattern, and engine speed on the nominal minimum film thickness, friction force, ad frictional power losses are investigated. As the roughness height increases, the nominal oil film thickness and total friction force increase. Also, the effect of the surface roughness on the boundary friction is dominant at low engine speed and high asperity height. The longitudinal roughness pattern shows lower mean oil film pressure and thinner oil film thickness compared to the case of the isotropic and transverse roughness patterns.